Simplify stdlib code by using itertools.batched()

[lgeiger]

#98364 introduced itertools.batched() but since it's pretty new it's still rarely used inside the standard library.

pickle.py includes a custom version multiple times which all could be replaced by itertools.batched() for improved readability.
This probably has a negligible performance impact (at the very least it won't be slower) but should make the code easier to understand.

Let me know if you're interested in a contribution for this or whether you'd rather not have the extra churn for a minor change like this.

[picnixz]

I'm not sure we want to refactor pickle.py, especially not the pure Python implementation. But I'll let this decision fall to @serhiy-storchaka.